The present invention relates to electrical connection in a printed wiring board venue, and especially to inter-board physical and electrical connection between wiring boards. Conventional inter-board physical and electrical connection between printed wiring boards is commonly effected using pins having a split, or xe2x80x9cC-shapedxe2x80x9d cross sectional configuration. A significant disadvantage of such pin connectors is that they commonly make physical and electrical contact only at three points within an aperture in a wiring board into which the pin is inserted. Moreover, such split pins commonly require high pressure fitting forces to ensure a tight fit within the mounting aperture. Hardened press pins overcome some disadvantages. For example, hardened press pins are able to better withstand high insertion pressures employed to press fit them into apertures. However, such hardened pins are expensive to manufacture. In this world in which cost advantages for high volume products are measured in fractions of pennies, it is desirable to avoid the expense of using hardened connector pins.
There is a need for an inexpensive interconnect apparatus and method for use in establishing physical and electrical connections between printed wiring boards that is installed with a relatively low force press fit. Most preferably, the interconnect apparatus should have high electrical conductivity and a high current-carrying capacity, on the order of 25 amperes or more. It is also preferable that the interconnect apparatus presents low electrical resistance. Most desirably an apparatus for interconnecting wiring boards will have a construction establishing a hermetically sealed structure resistant to corrosion and establishing a substantially complete electrical joint within a mounting aperture in order to reduce arcing and other sources of electromagnetic noise. It is desirable that such a connection apparatus be capable of operating at normal operating temperatures associated with operation of a power electrical circuit. In a particular embodiment of the invention, overheating of a circuit does not cause circuit failure because the connecting apparatus has a self-healing characteristic. In particular, the apparatus facilitates solder reflow to repair circuit anomalies caused by overheating.
An apparatus for connecting a plurality of electrical circuits borne upon a plurality of substrates is disclosed. At least a first substrate of the plurality of substrates has a first aperture having a first diametral displacement and a first inner wall. At least a portion of the first inner wall is electrically connected with a first circuit of the plurality of circuits borne upon the first substrate. The apparatus comprises a sheet of electrically conductive material arranged to a displacement from an axis in a substantially helical orientation about the axis. The material has a spring characteristic when the helical orientation establishes the displacement at a spring displacement. The spring characteristic urges the conductive material to a greater displacement from the axis than the spring displacement and permits insertion of the apparatus in the first aperture. The spring characteristic and the first diametral dimension cooperate to seat the apparatus in the first aperture to establish electrical connection with the first circuit.
A method for connecting a plurality of electrical circuits borne upon a plurality of substrates is also disclosed. At least a first substrate of the plurality of substrates has a first aperture having a first diametral displacement and a first inner wall. At least a portion of the first inner wall is electrically conductive and connected with a first circuit of the plurality of circuits borne upon the first substrate. The method comprises the steps of: (a) spirally winding a sheet of electrically conductive material to an insertion diametral displacement generally equal to or slightly greater than the first diametral displacement; and (b) urging the spirally wound sheet into the first aperture.
The method may comprise, following step (a), the further steps of: (1) depositing a plating mask material upon the electrically conductive material; (2) removing the plating mask from outside surfaces of the spirally wound material; and (3) plating the outside surfaces to enhance solderability of the outside surfaces.
In the preferred embodiment of the present invention, a roll pin construction is employed for a terminal to effect mechanical and electrical connection between printed wiring boards of an inter-board electrical circuit. Installation of the connection involves inserting the roll pin into a plated through-hole in one of the wiring boards, such as the wiring board carrying a power module circuit. The pin establishes a mechanical connection between the power module and another board, which may be supplied by a customer. The pin also established an electrical connection between the circuitry carried on the two wiring boards. The pin may or may not need to be soldered. Because of the spiral roll-up construction of the pin, and the spring bias thereby established in the pin, a nearly 360 degree connection between the pin and the interior wall of the plated through-hole is established. Such a nearly 360 degree connection provides low resistance, high current-carrying capacity and a near-hermetic sealed connection that reduces arcing and other electromagnetic noise sources. Soldering the pin-and-board assembly reflows solder between the pin and the wall of the through-hole to enhance the quality and completeness of the connection between the pin and board.
Prior art roll pins available at present are generally constructed of steel. The inventors found that steel roll pins exhibited too great a spring bias against the interior walls of through-holes and tended to fracture or break board material in the vicinity of the through-hole. Accordingly, the preferred embodiment of the present invention is fabricated of a bronze alloy. A bronze alloy retains sufficient mechanical characteristics to provide sufficient spring bias for carrying out the desired employment of the invention, and maintains appropriate electrical characteristics also.
The preferred embodiment of the present invention involves ensuring that no interstitial bonding material, such as solder, is present between layers of the spirally wound roll pin. Preferably, the interior of the roll pin is coated with a plating mask material to assure that no bonding material will be deposited between layers. Such an avoidance of interstitial bonding is preferred in order that the roll pin can exercise its spring bias imparted by spiral rolling to expand within a through-hole and establish the desired nearly 360 degree contact with the inner wall of the through-hole. Outside surfaces of the roll pin may have plating mask material removed and the exposed outside surfaces may be plated to permit bonding, such as soldering, between the roll pin and the inner wall of the through-hole.
An alternate embodiment of the present invention is constructed for self-healing properties in the event of overheating of the circuit in which the connector pin is included. In such an alternate embodiment, interior interstitial surfaces of the roll pin are intentionally plated and solderable, and solder material is intentionally introduced interstitially between the roll pin layers. In such an alternate construction, interstitially situated solder will reflow to heal connection rifts in the event of an overheating condition. Preferably, the alternate embodiment is installed before being exposed to a heated environment. After situating a roll pin with interstitial solder into an aperture, subsequent heating reflows the solder sufficiently to facilitate exercising the spring bias of the roll pin to establish a nearly 360 degree contact with the interior wall of the through-hole.
An advantage is provided by the present invention in assembling multi-board circuits because the firmly seated joint between the roll pin and a through-hole better assures a perpendicular relation between the pin and an associated board, or boards. Such a plumb orientation is important in through-hole-to-through-hole connections in which each board in a multi-board circuit is connected by a pin inserted into a through-hole.
A different multi-board joint arrangement, a through-hole-to-pad inter-board connection, is also provided with a more reliable plumb arrangement by the present invention,. In such an arrangement one board is connected with a pin-and-though-hole joint, generally of the sort described above. The second board presents a pad for bonded (e.g., solder) joining with the pin. Usually the pin has a pad structure to present a pad-to-pad bonding area. The firm physical fit of the near 360 degree contact between the pin and the inner wall of the through-hole of the first board maintains the pin in a desired orientation plumb with both boards during installation. The resultant finished joint construction is more reliably properly plumb after installation when the present invention is employed for multi-board connections.
It is, therefore, an object of the present invention to provide an apparatus and method for connecting a plurality of circuits borne upon a plurality of substrates that establish physical and electrical connection interconnections between substrates and require low pressing forces for assembly.
It is a further object of the present invention to provide an apparatus and method for connecting a plurality of circuits borne upon a plurality of substrates that has high conductivity and high current-carrying capacity.
It is yet a further object of the present invention to provide an apparatus and method for connecting a plurality of circuits borne upon a plurality of substrates that establishes an air-tight hermetic joint within a mounting aperture.
It is still a further object of the present invention to provide an apparatus and method for connecting a plurality of circuits borne upon a plurality of substrates that has a self-healing characteristic to repair circuit anomalies caused by overheating.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiment of the invention.